A post on the FlowPlayer.org forum says:
It is technically possible to stream YouTube videos directly with Flowplayer
... but doesn't give an example :(
Here is the related post: http://flowplayer.org/forum/7/17501
How can I use FlowPlayer to show YouTube videos?
I haven't used it, but here is a third party plugin: http://flowplayer.electroteque.org/youtube